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Rock Magnetic Cyclostratigraphy of Permian Loess in Eastern Equatorial Pangea (Salagou Formation, South-Central France)
Frontiers in Earth Science ( IF 2.9 ) Pub Date : 2020-06-03 , DOI: 10.3389/feart.2020.00241
Lily S. Pfeifer , Linda Hinnov , Christian Zeeden , Christian Rolf , Christian Laag , Gerilyn S. Soreghan

We present the findings from analysis and modeling of a stratigraphic series of magnetic susceptibility (MS) data measured with a portable MS meter from the Permian Salagou Formation loessite (south-central France). The results reveal discernible Milankovitch-scale paleoclimatic variability throughout the Salagou Formation, recording astronomically forced climate change in deep-time loessite of eastern equatorial Pangea. Optimal sedimentation rates are estimated to have ranged between 9.4 cm/kyr (lower Salagou Formation) and 13 cm/kyr (mid-upper Salagou Formation). A persistent 10-m-thick cyclicity is present that likely represents orbital eccentricity-scale (∼100 kyr) variability through the middle to late Cisuralian (ca. 285—275 Ma). Subordinate, higher frequency cycles with thicknesses of ∼3.3–3.5 and ∼1.8 m appear to represent obliquity and precession-scale variability. If the driver of magnetic enhancement is pedogenic, then the ∼10 m thick cyclicity that is consistent over ∼1000 m of section may represent the thickness of loessite–paleosol couplets in the Salagou Formation. Laboratory rock magnetic data show generally low magnetic enhancement compared to analogous Eurasian Quaternary loess deposits. This is related to the predominance of hematite (substantially weaker signal than magnetite or maghemite) in the Salagou Formation which may be explained by different conditions of formation (e.g., syn depositional processes, more arid, and/or oxidizing climate conditions) than in present Eurasia and/or post depositional oxidation of magnetite and maghemite.



中文翻译:

赤道东部Pangea(法国中南部萨拉古组)二叠纪黄土的岩石磁地层

我们提供了从二叠纪萨拉古组泥岩(法国中南部)的便携式质谱仪测量的地磁系列(MS)数据的分析和建模结果。研究结果揭示了整个萨拉古组的米兰科维奇尺度古气候变化,记录了赤道东部Pangea深层泥土的天文学强迫气候变化。最佳沉积速率估计在9.4 cm / kyr(较低的Salagou组)和13 cm / kyr(中上部Salagou组)之间。存在一个持续的10 m厚的周期性,这可能代表了中西奥拉期(约285-275 Ma)的轨道偏心尺度(〜100 kyr)的变化。从属的,更高频率的周期,其厚度为〜3.3-3.5和〜1。8 m似乎代表了倾角和进动规模的可变性。如果磁增强作用的成因是成岩作用的,那么在约1000 m的截面上一致的约10 m厚的周期性可能代表了Salagou组黄土-古土壤耦合的厚度。与类似的欧亚第四纪黄土矿床相比,实验室岩石磁数据通常显示出较低的磁增强作用。这与萨拉古组中赤铁矿的优势(比磁铁矿或磁赤铁矿的信号弱得多)有关,这可以用比目前不同的形成条件(例如同沉积过程,更干旱和/或氧化的气候条件)来解释。欧亚大陆和/或磁铁矿和磁赤铁矿的沉积后氧化。那么大约1000 m的剖面上约10 m厚的循环性可能代表了萨拉沟组黄土-古土壤耦合的厚度。与类似的欧亚第四纪黄土矿床相比,实验室岩石磁数据通常显示出较低的磁增强作用。这与萨拉古组中赤铁矿的优势(比磁铁矿或磁赤铁矿的信号弱得多)有关,这可以用与目前不同的形成条件(例如同沉积过程,更干旱和/或氧化的气候条件)来解释。欧亚大陆和/或磁铁矿和磁赤铁矿的沉积后氧化。则在约1000 m的剖面上约10 m的周期性是一致的,这可能代表了萨拉沟组黄土-古土壤耦合的厚度。与类似的欧亚第四纪黄土矿床相比,实验室岩石磁数据通常显示出较低的磁增强作用。这与萨拉古组中赤铁矿的优势(比磁铁矿或磁赤铁矿的信号弱得多)有关,这可以用与目前不同的形成条件(例如同沉积过程,更干旱和/或氧化的气候条件)来解释。欧亚大陆和/或磁铁矿和磁赤铁矿的沉积后氧化。与类似的欧亚第四纪黄土矿床相比,实验室岩石磁数据通常显示出较低的磁增强作用。这与萨拉古组中赤铁矿的优势(比磁铁矿或磁赤铁矿的信号弱得多)有关,这可以用与目前不同的形成条件(例如同沉积过程,更干旱和/或氧化的气候条件)来解释。欧亚大陆和/或磁铁矿和磁赤铁矿的沉积后氧化。与类似的欧亚第四纪黄土矿床相比,实验室岩石磁数据通常显示出较低的磁增强作用。这与萨拉古组中赤铁矿的优势(比磁铁矿或磁赤铁矿的信号弱得多)有关,这可以用与目前不同的形成条件(例如同沉积过程,更干旱和/或氧化的气候条件)来解释。欧亚大陆和/或磁铁矿和磁赤铁矿的沉积后氧化。

更新日期:2020-06-26
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